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Gastrointestinal > GI 1 > Flashcards

GI 1 Flashcards

1
Q

What is the function of the colon?

A
  • Reabsorbs fluids and electrolytes

- Stores faecal matter before delivery to the rectum

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2
Q

What are the four layers of the digestive tract wall?

A

1) Mucosa
2) Submucosa
3) Muscularis externa
4) Serosa

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3
Q

What produces motility in the GI tract?

A
  • Gap junctions produce synchronous waves between coupled cells
  • Spontaneous electrical activity from Interstitial Cells of Cajal (ICCs)
  • Modulated by intrinsic and extrinsic NS and hormones
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4
Q

How do ICCs work?

A
  • Form bridge between plexus nerve endings and smooth muscle cells
  • Contraction occurs when slow wave amplitude reaches threshold
  • Force related to duration that slow wave is above threshold
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5
Q

How does peristalsis occur?

A
  • Distension of gut activates sensory neurones
  • Altered activity of interneurones and motoneurones
  • Longitudinal/circular muscle relax + contract
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6
Q

What are the major motility patterns in the GI tract?

A

1) Peristalsis
2) Segmentation
3) Colonic mass movement
4) Migrating motor complex (MMC)
5) Tonic/sustained contractions

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7
Q

What is gluconeogenesis?

A

The de novo synthesis of glucose from metabolic precursors (lactate, amino acids, glycerol); primary source of glucose overnight, but energetically expensive

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8
Q

Describe the process of glycogen breakdown

A

1) Glycogen -> G1P by glycogen phosphorylase (RLS)
2) G1P -> G6P by phosphoglucomutase
3) G6P -> glucose in liver by glucose-6-phosphatase or to glycolysis

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9
Q

Why is fat required in the diet?

A
  • Fat-soluble vitamins
  • Essential fatty acids
  • As an energy source
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10
Q

What are the main products of fat digestion?

A

1) Glycerol; readily absorbed into epithelial cells
2) FAs; short&med enter portal blood
3) Monoglycerides; with long FAs -> triglycerides

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11
Q

What are chylomicrons?

A

Absorbed fats coated with a layer of protein, phospholipid or cholesterol; enter lymph -> bloodstream -> muscle and adipose tissue -> attacked and cleaved by lipoprotein lipases -> provide energy/storage

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12
Q

What epithelium is found in the oral cavity, oropharynx and laryngopharynx?

A

Non-keratinised stratified squamous epithelium

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13
Q

What epithelium is found in the nasal cavity and nasopharynx?

A

Respiratory epithelium // ciliated columnar epithelium

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14
Q

Describe the epithelium on the anterior 2/3rds of the tongue

A

Stratified squamous epithelium; thin on ventral surface and thick with papillae on dorsal surface

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15
Q

Describe the epithelium on the posterior 1/3 of the tongue

A

Smooth stratified squamous epithelium which, except for the circumvallate papillae, lacks papillae but does have substantial lymphoid aggregates in the submucosa

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16
Q

What occurs at the gastro-oesophageal junction?

A

The abrupt transition from stratified squamous epithelium of oesophagus to the simple columnar epithelium of the cardia of the stomach

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17
Q

Describe the distribution of cells in the gastric pit

A

1) Isthmus (stem) - parietal cells and stem cells
2) Neck (junction) - mucous cells and parietal cells
3) Fundus (base) - mostly chief cells; also parietal and neuroendocrine cells

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18
Q

What is the difference between chief and parietal cells of the gastric glands?

A
  • Chief cells are digestive enzyme secreting cells

- Parietal cells are hydrochloric acid producing cells

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19
Q

What is different about the muscular externa of the stomach?

A

It contains an additional layer which is oblique and internal to the circular muscle layer; it aids the churning action of the stomach

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20
Q

What occurs at the gasproduodenal junction?

A

An abrupt transition from stomach mucosa to duodenal mucosa; the inner circular layer of smooth muscle to thickened to form the pyloric sphincter

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21
Q

Describe the duodenum of the small intestine

A

25cm long; contains Brunner’s glands in the submucosa

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22
Q

Describe the jejunum of the small intestine

A

2m long; tallest villi, located on permanent circular folds of the mucosa and submucosa, the plicae circularis; lymphoid follicles infrequent

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23
Q

Describe the ileum of the small intestine

A

2.75m long; characterized by shorter villi and aggregations of lymphoid follicles called Peyer’s patches found in the submucosa and often extending into the lamina propria

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24
Q

What occurs at the rectoanal junction?

A

Distinct junction between the mucosa of the rectum and the non-keratinized stratified squamous epithelium of the anal canal which is continuous with the keratinized stratified squamous epithelium of the surrounding skin

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25
Q

What is the function of the liver?

A
  • Synthesis and secretion of bile
  • Synthesis of special proteins
  • Detoxification
  • Storage of glycogen, vitamins and iron
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26
Q

Describe the structure of the liver

A

Made up of hexagonal segments called lobules with a branch of the portal vein in the centre and a portal triad at each corner; hepatocytes form sheets with spaces for blood channels called sinusoids

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27
Q

What is the space of Disse/perisinusoidal space?

A

A narrow space between the lining endothelial cells of sinusoids and the hepatocytes

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28
Q

What are hepatic stellate cells (Ito cells)?

A

Found scattered in the space of Disse; modified fibroblasts + make CT; store vitamin A within fat droplets in their cytoplasm; can transform into myofibroblasts to make scar tissue

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29
Q

What are Kupffer cells?

A

Macrophages found within sinusoids which remove worn out red blood cells and particulate matter from the blood

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30
Q

How is bile produced?

A

Hepatocytes produce bile which flows via bile cannaliculi to bile ducts and then to hepatic ducts

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31
Q

What is the function of the gall bladder?

A

To store and modify bile received from the liver

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32
Q

Describe the structure of the gall bladder

A

A muscular sac lined by simple columnar epithelium, a lamina propria of loose connective tissue rich in blood vessels and lymphatic vessels, a coat of smooth muscle and an outer collagenous layer of adventitia

33
Q

What is the function of the pancreas?

A
  • Endocrine: small scattered islands of tissue which produce insulin and glucagon to regulate blood sugar
  • Exocrine: produces pre-enzymes and digestive juices to break down proteins, lipids, DNA, RNA etc.
34
Q

What is lipogenesis?

A
  • Reductive process which is de novo synthesis of fatty acids occurring in liver, kidney, mammary glands, adipose tissue and the brain
  • Takes place during excess energy intake
35
Q

What is the formula for lipogenesis?

A

Dietary starch -> glucose -> pyruvate -> acetyl-coA -> malonyl-coA -> fatty acids -> triglycerides

36
Q

Why is amino acid degradation needed?

A

There is no storage form for amino acids

37
Q

What are the steps of amino acid degradation?

A
  • Takes place in the liver
    1) Absorption - by intestinal cells and released into blood
    2) Protein turnover - tightly regulated, differing rates, damages proteins removed
38
Q

What are the major-nitrogen containing excretory molecules

A

1) Urea
2) Uric acid
3) Creatinine
4) Ammonium ions

39
Q

What is the formula for BMI?

A

Weight (kg) / square of height (m) = BMI

40
Q

What are the reference ranges for BMI?

A
  • Up to 25 = thin/normal
  • 25.0 - 29.9 = overweight
  • 30.0 - 39.9 = obese
  • 40+ = morbidly obese
41
Q

What are some satiation signals?

A
  • Cholecystokinin (CCK)
  • Peptide YY (PYY3-36)
  • Glucagon-like peptide 1 (GLP1)
  • Oxyntomodulin (OXM)
  • Obestatin
42
Q

What 2 hormones inform the brain to alter energy balance (↓less, ↑burn)?

A
  • Leptin -> made and released from fat cells

- Insulin -> made and released from pancreatic beta cells

43
Q

Why can leptin-therapy not be used in diet-induced obesity (DID)?

A

Severe leptin resistance due to:

1) Defective leptin transport into the brain
2) Altered signal transduction following leptin binding to its receptor

44
Q

What is brown adipose tissue?

A
  • Known as the ‘good fat’

- Main function is to turn food into body heat

45
Q

What occurs in the orad region of the stomach?

A
  • Fundus and proximal body
  • No slow wave activity
  • Relatively weak maintained tonic contractions of about 1 min, lasting for an hour
46
Q

What occurs in the caudad region of the stomach?

A
  • Distal body and antrum
  • Phasic intermittent contractions
  • Slow waves occur continuously (3 min-1) but only those reaching threshold elicit contraction
  • Retropulsion mixes gastric contents, grinding chyme
47
Q

How does gastric distension increase motility?

A

1) Stretch of smooth muscle
2) Simulation of intrinsic nerve plexuses
3) Increased vagus nerve activity and gastrin release

48
Q

What factors control the strength of the antra wave and determine stomach emptying?

A

1) Rate of emptying proportional to volume of chyme in stomach
2) Consistency of chyme
3) Duodenum must be ready to recieve chyme

49
Q

What secretions come from oxyntic (fundus and body) gastric mucosa?

A
  • HCl
  • Pepsinogen
  • Intrinsic factor and gastroferrin
  • Histamine
  • Mucus
50
Q

What secretions come from pyloric (distal stomach and antrum) gastric mucosa?

A
  • Gastrin
  • Somatostatin
  • Mucus
51
Q

What secretagogues induce hydrochloric acid secretion from the parietal cell?

A

1 - Acetylcholine (ACh)
2 - Gastrin
3 - Histamine

52
Q

What inhibits hydrochloric acid secretion from parietal cells?

A

1 - Somatostatins

2 - Prostaglandins

53
Q

What are the three phases of gastric acid secretion?

A

1) Cephalic - preparation by CNS and vagus nerves
2) Gastric - during, physical and chemical mechanisms
3) Intestinal phase - after, neuronal and hormonal mechanisms

54
Q

What liquids are received by the small intestine?

A
  • Chyme from the stomach
  • Bile from the liver and gallbladder
  • Pancreatic juice from the pancreas
55
Q

How does mixing and propulsion of chyme occur in the small intestine?

A

1) Segmentation after meal - chopping moves chyme back and forth by alternating contraction and relaxation of circular muscle
2) Peristalsis when fasting - localised contractions and MMC

56
Q

What is the migrating motor complex?

A
  • Strong peristaltic contraction slowly passing length of the intestine every 90 - 120 mins
  • Clears small intestine of debris, mucus and sloughed epithelial cells between meals
57
Q

What hormones are secreted by the small intestine?

A
  • Secretin from S cells
  • Gastrin from G cells
  • Cholecytokinin (CCK) from I cells
  • Gastric inhibitory peptide (GIP) from K cells
  • Glucagon like peptide 1 (GLP1) from L cells
  • Motilin from M cells
  • Ghrelin from Gr cells
58
Q

What are the control mechanisms of the succus entericus?

A
  • Distension/irritation (↑)
  • Gastrin (↑)
  • Cholecystokinin (CCK) (↑)
  • Secretin (↑)
  • Parasympathetic nerve activity (↑)
  • Sympathetic nerve activity (↓)
59
Q

What are the components of the success entericus of the small intestine?

A
  • No digestive enzymes
  • Mucus for protection/lubrication - by goblet cells
  • Aqueous salts for enzymatic digestion - by crypts of Lieberkuhn
60
Q

What are the pancreatic secretions?

A

1) Endocrine - insulin and glucagon to the blood
2) Exocrine - digestive enzymes (acinar cells) and aqueous NaHCO3- solution (duct cells) make up pancreatic juice, released to duodenum

61
Q

How is pancreatic secretion controlled?

A

1) Cephalic - vagal stimulation of A cells
2) Gastric - vasovagal reflex -> parasympathetic stimulation of A and D cells
3) Intestinal - acid/fat/protein in duodenal lumen

62
Q

What are the two types of digestive processes in the small intestine?

A

1) Luminal digestion - mediated by pancreatic enzymes secreted into the duodenum
2) Membrane digestion - mediated by enzymes situated at the brush border of epithelial cells

63
Q

What is the sequence of carbohydrate digestion?

A

Polysaccharides (intraluminal hydrolysis) -> oligosaccharides (membrane digestion) -> monosaccharides (absorption)

64
Q

Describe protein digestion in the stomach

A
  • HCl begins to denature proteins

- Pepsin is an endopeptidase which cleaves proteins into peptides, has a preference larger neutral amino acids

65
Q

What are the five pancreatic proteases?

A

1) Trypsin
2) Chymotrypsin
3) Elastase
4) Procarboxypeptidase A
5) Procarboxypeptidase B

66
Q

Describe protein digestion in the duodenum

A

The five pancreatic proteases are secreted as proenzymes from the acinar cells of the exocrine pancreas and converted to active form in the duodenum; They function as either endopeptidases, or exopeptidases

67
Q

What are the additional proteases which aid protein digestion other than pancreatic proteases?

A

1) Brush border peptidases

2) Cytoplasmic peptidases

68
Q

How are amino acids absorbed?

A
  • At brush border, 7 different mechanisms; 5 are secondary active transport; 2 Na+ independent
  • At basolateral membrane, 5 different mechanisms; 3 mediate efflux of amino acids; 2 mediate influx
69
Q

How are di-, tri- and tetra-peptides absorbed?

A
  • Via H+-dependent mechanism at brush border (co-transport) pump is PepT1
  • Further hydrolysed to amino acids within the enterocyte
  • Na+-independent systems at the basolateral membrane (facilitated transport)
70
Q

In what 3 ways does emulsification of ingested lipids occur?

A

1) Mouth - chewing
2) Stomach - gastric churning and squirting through narrow pylorus; content mixed with digestive enzymes from mouth and stomach
3) Small intestine - segmentation and peristalsis mix the luminal content with the pancreatic and biliary secretions

71
Q

Describe the stabilisation of emulsion drops of ingested lipids

A
  • Stabilised by the addition of a ‘coat’ of amphiphilic molecules that form a surface layer on the droplets
  • Provide a vast increase in the surface area to volume ratio at which digestion by lipases and other esterases can accomplish digestion
72
Q

What is the role of bile salts in the digestion of lipase?

A
  • Emulsify large lipid droplets into small droplets

- Increase surface area for attack by pancreatic lipase

73
Q

What is colipase and what is its role in lipid digestion?

A
  • An amphipathic polypeptide secreted with lipase by the pancreas
  • Binds to bile salts and lipase allowing lipase access to tri- and di-acylglycerols
74
Q

How are digested lipids absorbed into small intestine cells?

A
  • Lipid mixed micelles enter by passive diffusion/transport proteins
  • Short and medium chain fatty acids enter through diffusion
  • Long chain fatty acids are resynthesises into chylomicrons and carried in lymph to systemic circulation
  • Cholesterol is transported by endocytosis in clatherin-coated pits
75
Q

How is iron absorbed into small intestine cells?

A
  • Reduced from Fe3+ to Fe2+ by accepting an e-
  • Fe2+ absorbed across apical membrane by transport processes
  • Conveyed to basolateral membrane via a molecular chaperone and trasported across by transporters
  • Oxidised to Fe3+ and transported into tissues
  • Imported across apical membrane; cytoplasmic metabolism to release Fe2+
76
Q

How is vitamin B12 absorbed into small intestine cells?

A

Ingested in food bound to proteins -> stomach acid removes protein -> haptacorin binds to vitamin in stomach -> stomach parietal cells release intrinsic factor -> pancreatic proteases digest haptacorin in stomach -> vitamin B12 released -> bind to intrinsic factor in small intestine -> vitamin B12-intrinsic factor complex absorbed in terminal ileum by endocytosis

77
Q

How are fat-soluble vitamins absorbed into small intestine cells?

A
  • Incorporated into mixed micelles and passively transported into enterocytes or
  • Incorporated into chylomicrons/VLDL’s and distributed by intestinal lymphatics
78
Q

How are water-soluble vitamins absorbed into small intestine cells?

A

Transport processes in the apical membrane which may be either Na+-dependent, or Na+-independent

Gastrointestinal (8 decks)

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